Clipper circuits, also called limiters, are designed to limit the
signal swing. They are often used at the input of a system to protect
the system from overvoltage. When clipping occurs, the shape of the
waveform is changed. Circuits designed to respond to frequency
variations often use limiters to clip the signal and remove unwanted
amplitude variations. For example, FM radio system use frequency
variations to transfer information. Therefor, one of the first circuits
in an FM radio receiver is a limiter circuit that removes the unwanted
amplitude variations but keeps the frequency variations. Clipper
circuits use diodes to perform the clipping. If the diode is in series
with the load, the circuit is called a series clipper. If the diode is
in parallel with the load, the circuit is called a parallel clipper.